Homo- and heterodinuclear luminescent helicates

Abstract

The specific photophysical properties of the NIR-emissive lanthanide-based complexes attract much attention due to the potential applications in medical diagnostic and optoelectronics. On the other hand, luminescent helicates are in the focus of attention of supramolecular chemistry. In this thesis, the self-assembly principles are applied to prepare mono- and dinuclear lanthanide(III)-containing systems using 8-hydroxyquinoline and its derivatives as building blocks. First, effective pathways for the synthesis of ligands possessing appropriate (bi-, tri-, tetradentate) chelating units were elaborated. Thus, 8-hydroxyquinolines bearing a semicarbazone or SAMP hydrazone group perform in a tetradentate manner; moreover the former tend to agglomeration during complex isolation in the solid state. In contrary, the imine, carboxamide, carboxylate, and imidate donor functions implemented in the 2-position of the quinoline core provide nine coordination at the metal center upon binding of three such strands in the complexation step. The Hiratani-double-Claisen rearrangement is proposed as a key synthetic transformation to extend the helicating motif over the longer ligand sequence. Moreover the applicability of a wide range of substrates to this protocol allows a combination of tridentate (for addressing f-elements) and bidentate (for the recognition of p-/d-block metals) binding compartments within a single segmental receptor. The coordination studies were performed towards the rare-earth(III) elements in order to establish the binding ability of novel quinolinate receptors. Monometallic model systems were characterized by X-ray diffraction analysis in the solid phase and by NMR and ESI MS in solution. Tridentate units are found to be optimal providing tight ligand environment around the incorporated emitter which is especially valuable from the spectroscopic point of view. The photophysical properties of the monometallic compounds were determined in the solid state showing efficient sensitization of the NIR luminescence from Nd(III), Er(III), Yb(III) complexes of 2-amidoquinolinate ligands. The effect of bromination on the spectroscopic parameters (quantum yield and lifetime) was observed upon successive introduction of the halogen substituents on the ligand scaffold. Next, the symmetric and unsymmetric ditopic receptors were involved in the coordination investigations. The selective recognition of p-, d-, and f-elements by discrete binding domains of a single strand furnished homo- and heterodinuclear helicate-type compounds in which intramolecular intermetallic communication is remarkably facilitated and enabled to control by tuning the metal-metal separation. The speciation in solution was monitored by 1H NMR spectroscopy, ESI MS, and spectrophotometric titration. In parallel, the template effect was observed by means of X-ray diffraction analysis as the decisive factor governing self-organization processes which occur in solution. The homo- Yb/Yb and heterodinuclear Yb/Al helicates were employed to study energy transfer processes occurring between different complex fragments of one supramolecular edify connected by flexible isobutenylidene spacer. Thus, the intrinsic deactivation of the green emission of the chromophore of the Yb/Al probe followed by energy transfer to the emissive states of the lanthanide(III) compartment results in the significant improvement of the Yb-centered luminescence in the solid phase. Also the bis-amide bridged symmetrical ligands were involved in the coordination studies. In these systems the stereocontrol and rigidity are attained by altering the nature of the spacer between binding sites. In addition, low energy chromophores (N-containing heterocycles) were attached to the quinoline ligand in order to be further involved in the coordination of NIR emitting lanthanide(III) ions as suitable sensitizers of luminescence at longer wavelengths. The synthetic procedures for the preparation of tri- and tetratopic ligands predisposed for the insertion of several metal centers, particularly lanthanide(III) ions, in the elongated helicates were developed, thus offering excellent approach to the multifunctional luminescent probes. Finally, the applicability of the microwave technology to the construction of substituted quinolinol derivatives was demonstrated on the Combes, Conrad-Limpach, and Gould-Jacobs methods yielding 4-quinolones in a two-step one-pot reaction